An electrophoretic display (EPD) is a non-emissive device based on the electrophoresis phenomenon influencing charged pigment particles suspended in a dielectric solvent. An EPD typically comprises a pair of spaced-apart plate-like electrodes. At least one of the electrode plates, typically on the viewing side, is transparent. An electrophoretic fluid composed of a dielectric solvent with charged pigment particles dispersed therein is enclosed between the two electrode plates.
When a voltage difference is imposed between the two electrode plates, the pigment particles migrate by attraction to the plate of polarity opposite that of the pigment particles. Thus, the color showing at the transparent plate can be either the color of the solvent or the color of the pigment particles. Reversal of plate polarity will cause the particles to migrate back to the opposite plate, thereby reversing the color.
An electrophoretic display as described has certain disadvantages. For example, in the dark color state while the light-colored pigment particles are at the bottom of a display cell (opposite from the viewing side), the dark-colored dye in the display fluid cannot absorb all of the incoming light. As a result, some of the incoming light would penetrate through the dark-color fluid and strike the light-colored pigment particles and then reflect back to the viewer. This will increase the reflectance of the dark state and lower the contrast of the images displayed.